CVE-2013-0340 in tvOS
Summary
by MITRE
expat before version 2.4.0 does not properly handle entities expansion unless an application developer uses the XML_SetEntityDeclHandler function, which allows remote attackers to cause a denial of service (resource consumption), send HTTP requests to intranet servers, or read arbitrary files via a crafted XML document, aka an XML External Entity (XXE) issue. NOTE: it could be argued that because expat already provides the ability to disable external entity expansion, the responsibility for resolving this issue lies with application developers; according to this argument, this entry should be REJECTed, and each affected application would need its own CVE.
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Analysis
by VulDB Data Team • 11/29/2025
The vulnerability identified as CVE-2013-0340 represents a critical XML External Entity (XXE) flaw within the expat XML parser library prior to version 2.4.0. This issue stems from the library's inadequate handling of entity expansion processes, creating a pathway for malicious actors to exploit resource consumption vulnerabilities through carefully crafted XML documents. The vulnerability operates at the core parsing layer of XML processing, where the parser fails to properly validate or restrict external entity references without explicit developer intervention through the XML_SetEntityDeclHandler function. This design flaw fundamentally compromises the security posture of applications relying on expat for XML processing, as it enables attackers to manipulate the parsing behavior in ways that were not intended by the library's original security model.
The technical exploitation of this vulnerability manifests through multiple attack vectors that demonstrate the severity of the XXE issue within the expat library. Remote attackers can leverage this weakness to consume excessive system resources, effectively creating a denial of service condition that can bring applications to their knees through resource exhaustion attacks. Additionally, the vulnerability enables attackers to send HTTP requests to internal intranet servers, effectively bypassing network segmentation controls and potentially exposing internal systems to unauthorized access. The most concerning aspect involves the ability to read arbitrary files from the filesystem, which can lead to information disclosure attacks and potentially complete system compromise. The vulnerability specifically targets the XML parsing mechanism where external entity references are processed, allowing attackers to construct XML documents that trigger unintended file system operations or network communications.
The operational impact of CVE-2013-0340 extends far beyond simple denial of service scenarios, as it fundamentally undermines the security controls that applications rely on for protecting sensitive data and internal systems. Applications using vulnerable versions of expat become susceptible to attacks that can bypass traditional security controls, including firewalls and network segmentation, by leveraging the XML parsing functionality to access internal resources. This vulnerability particularly affects web applications, APIs, and services that process untrusted XML input, creating a significant risk for organizations that have not implemented proper XML security measures. The impact is amplified because the vulnerability exists at the library level rather than in individual applications, meaning that a single vulnerable library can affect multiple applications across an organization's infrastructure. Organizations may face regulatory compliance issues and potential data breaches when applications are compromised through this XXE vulnerability.
Mitigation strategies for CVE-2013-0340 must address both immediate remediation and long-term architectural security improvements. The most effective immediate solution involves upgrading to expat version 2.4.0 or later, which includes proper entity handling mechanisms that prevent the exploitation patterns described in the vulnerability. Organizations should also implement XML security configurations that disable external entity processing entirely, which aligns with the CWE-611 weakness classification for improper restriction of XML external entities. Security teams should consider implementing application-level protections such as XML schema validation, input sanitization, and regular security testing to prevent exploitation attempts. The ATT&CK framework categorizes this vulnerability under the technique of "Server-Side Request Forgery" and "Resource Exhaustion" attacks, emphasizing the need for comprehensive network monitoring and intrusion detection systems. Additionally, developers should follow secure coding practices that include explicit entity handling configuration and regular security assessments to prevent similar vulnerabilities from emerging in future implementations.